There are many pathologies that can lead to loss of function of the foot and ankle. By way of example, these include stroke, diabetes, Muscular dystrophy, multiple sclerosis and peripheral vascular disease, as well as others. Often the biomechanical deficit will involve loss of dorsiflexion, i.e. the loss of ability to bring the foot up. This situation is generically known as drop foot.
The traditional solution is to provide a brace commonly known as an Ankle Foot Orthosis (AFO). The orthosis is commonly made out of one piece of plastic which is trimmed in the back so that it becomes flexible. This design is commonly known in the art as a Posterior Leaf Spring AFO.
An improved orthosis is an articulated AFO. This orthosis has an upper portion (calf section) connected to a lower portion (foot section) by a joint. The joint is internally or externally spring loaded so that it picks up the foot. For a spastic patient, a range limiting joint design may be indicated. A range limiting joint limits the patients' ability to push the foot down (plantarflex) beyond a predetermined angle. The articulated design allows a better biomechanical movement of the foot.
U.S. Pat. No. 5,826,304 to Carlson describes a composite flexure unit for hingedly joining two relatively movable parts. The unit includes a flexure member comprising a low modulus of elasticity material. The flexure has two mounting portions and a middle connecting portion. The flexure is bendable for pivoting about a rotational axis passing through the middle portion. A load bearing element comprises a high modulus of elasticity material for providing longitudinal strength and stiffness, without significantly increasing flexion stiffness about the rotational axis. An improvement over the Carlson patent is known and marketed under the trade name Tamarak Variable Assist™ Joint, (available from Tamarack Habilitation Technologies, Inc, Blaine, Minn., USA) wherein an adjustable hinge is added to one of the mounting portions, to allow mounting the flexure unit at adjustable angles to a portion of the brace.
U.S. Pat. No. 4,665,904 to Lerman discloses a supportive brace includes lateral and medial circular hinges rotatably securing the lateral and medial sides of the leg-supporting shell to the foot supporting shell. The circular hinges are formed by relatively large area wall portions of the shells which overlie each other in the vicinity of the ankle bones projected from the lateral and medial sides of the ankle.
It is therefore desired to provide a mechanism of adjustability of the joint characteristics that can easily tailored to individual patient needs such for example by the health care practitioner. Two degrees of adjustability are desired: the angle from which the plantarflexion preloading begins and the moment of force that is created from the preloading. An articulated AFO design that allows this adjustability is biomechanically desired for two important reasons: shock absorption at heel contact and knee stability at heel contact. During ambulation the first part of the step is when the heel hits the ground and the foot plantarflexes to what is generally referred to as footflat. At that first part, it is desirable to adjust the amount of resistance to plantarflexion according to individual needs, as without such resistance there is little to no shock absorption. On the other hand, an excessive resistance to plantarflexion will force the knee forward, resulting in a less stable biomechanical situation. The present invention provides easy adjustability, in an easy to manufacture design, which is cost efficient to manufacture.
An orthosis made of two parts presents a problem where, upon sliding the foot into the orthosis, the foot painfully hits, or otherwise gets snagged by, the foot portion. Certain aspects of the present invention aim to resolve this problem.